This invention relates to seismic exploration and more particularly to exploration in which it is desired to suppress ghost reflections caused by downwardly travelling rarefaction waves.
Land and marine seismic exploration have conventionally used geophones or hydrophones which produce an output in response to pressure. U.S. Pat. No. 3,346,838, Johnson III et al is an example of a pressure sensitive detector.
Another type of detector responds to the velocity of the particles of the medium surrounding the detector. In U.S. Pat. No. 2,982,942 White, three velocity-sensitive detectors 11, 12 and 13 are mounted at a listening station. The pressure-sensitive detector 15 is positioned at the same location. The signals from these detectors indicate the amplitude and direction of the acoustic energy impinging upon the detectors.
In seismic exploration, energy is reflected from subsurface interfaces and is detected to produce seismograms. It is desired to record only primary reflections which are upwardly travelling compressional waves caused by a reflection of the seismic energy from a subsurface interface. Other reflections such as multiple and ghost reflections obscure the seismogram. One particularly troublesome reflection is a ghost reflected from the surface. The ghost reflection travels downwardly as a rarefaction wave.